Background: According to a model of a fixed information processing capacity,
it was predicted that in a group of patients with CFS, high body
consciousness in combination with a high report of somatic symptoms would
affect information-processing speed negatively.

Methods: Information- and motor-processing speed were simultaneously measured
with a simple- and a choice-reaction time task, whereas cognitive complaints
were rated with two questionnaires. The hypothesized influence of private
body consciousness and somatic symptom report upon information-processing
speed was tested in a model. A symptom-validity test was used to screen for
possible illness behavior.

Conclusions: Levels of private body consciousness directly affected somatic
symptom report and information-processing speed. This finding supports the
role of attentive processes in CFS, and offers, besides possible cerebral
dysfunction, an alternative explanation for slowing of information processing
in CFS.
Chronic Fatigue Syndrome (CFS) is a medically unexplained clinically defined
condition, characterized by long-lasting (at least 6 months) severe disabling
fatigue, and a combination of at least four out of eight symptoms (1). One of
these eight major symptoms is self-reported impairment in concentration and
short-term memory. Despite the fact that many patients with CFS report
problems with concentration and memory, neuropsychological findings are not
consistent (2-10). Recent reviews suggested that these varying results were
caused by differences in diagnostic criteria for CFS, the heterogeneity of the
CFS population, small sample sizes or methodological diversity (11,12). In a
recently published study we also found evidence that the neuropsychological
test performance in comparative studies could have been biased by illness
behavior (13). Despite these possible confounders, a possible reduction in
information processing speed has been reported most consistently (11,12).

In a tested model for CFS, focusing on bodily symptoms, as measured by high
somatic symptom report, turned out to be strongly related to both fatigue
severity and experienced disability (14). Several studies showed that a wide
variety and high frequency of somatic symptoms characterized patients with
CFS. Compared with patients with multiple sclerosis or depression, patients
with CFS reported significantly more somatic symptoms on the somatization
subscale of the Symptom Checklist-90 (14-16). These findings suggested a
heightened bodily self-awareness in CFS.

In the literature, the following two constructs of self-focused attention have
been distinguished: private self-consciousness and private body consciousness
(17,18). Private self-consciousness relates to the tendency to attend to inner
psychological or emotional processes, whereas private body consciousness
reflects the person's sensitivity to perceive internal bodily sensations.
Several studies showed that private body consciousness was related to symptom
report and symptom severity, problem solving and attentional processing
(19-21).

A recent study, using 57 nonclinical subjects, demonstrated that a heightened
selective attentional focus on the body and the degree of symptom report
predicted levels of illness anxiety (23). A small, though significant,
relation was found between performance on a continuous performance test,
measuring visual sustained attention, and the extent subjects reported private
body consciousness. Higher levels of private body consciousness were
associated with a lower sensitivity index of the continuous performance test.
Based on their findings the authors hypothesized that bodily preoccupation
seemed to interfere with external task demands, making less attentional
resources available for processing of external information.

Martin et al (24) studied the relation between private body consciousness and
state anxiety in the report of somatic symptoms during a clinical magnetic
resonance imaging (MRI) investigation. They found that state anxiety and
private body consciousness interacted to predict the report of symptoms during
the MRI procedure. These findings were explained using the
information-processing model of Ahles et al (25). According to this model,
anxiety interacts with the predisposition to focus on bodily sensations by
increasing the likelihood that these sensations will be processed affectively.
This type of affective processing amplifies the somatic sensations, which are
then experienced and reported as symptoms.

Klein et al (22) assessed in 45 students whether a fixed-capacity
information-processing model could be used to explain the relationship between
problem-solving errors and life stress as moderated by anxiety and private
body consciousness. The data showed that high state anxiety in combination
with high life stress affected the performance on an analogical reasoning task
negatively, especially in subjects with high levels of private body
consciousness. It was concluded that stressful life events, and the
task-irrelevant thinking that characterizes state anxiety, occupied some
portion of a finite processing capacity. Furthermore, the authors reasoned
that anxiety is often accompanied with somatic sensations and that subjects
who have high levels of private body consciousness will be more attentive to
these sensations, leaving them with even less recourse for cognitive demanding
tasks.

The aforementioned studies suggested that private body consciousness was
associated with increased focusing on bodily sensations and higher somatic
symptom report, and might affect decision-making and information processing
capacity negatively. Therefore, the objective of the current study was to test
a model that incorporated both body consciousness and the extent patients
report somatic symptoms. Body consciousness was considered an independent
predisposing factor for the detection and subsequent report of somatic
symptoms, whereas it was assumed that the report of somatic symptoms could
also represent underlying psychosocial processes. According to the reports in
the literature, body consciousness was hypothesized to directly influence
information-processing speed, especially in subjects that are characterized by
high somatic symptom report. Because the somatic symptom report could involve
different causal processes, such as active focusing on bodily sensations,
anxiety, or perhaps even some form of illness behavior, the influence of
somatic symptom report upon neuropsychological test-performance was expected
to be less specific and not only to be limited to information processing
speed. Therefore, the model was also tested with motor-speed measures and
measures of self-reported cognitive complaints. To control for the possibility
of response bias influencing both neuropsychological performance and
interrelations between variables, the proposed models were tested for the
sample that showed valid performance on a symptom validity task.
MATERIALS AND METHODS

Subjects
This study was conducted at the Department of Medical Psychology of the
University Medical Center Nijmegen, the Netherlands. Complete data were
collected in 57 (44 females and 13 males) patients with a Center for Disease
Control and Prevention diagnosis of CFS, aged between 16 and 56 years, and
fulfilling operational criteria for fatigue severity and disability. Informed
consent was obtained before the start of the study (1). The mean age of this
group was 34.7 years and the mean illness duration was 1.9 years (range, 1 to
4 years).

Instruments
Private Body Consciousness
The subscale private body consciousness of the Body Consciousness
Questionnaire was used to measure this concept (26). This subscale has 5 items
that can be answered on a scale that ranged from 0 (extremely
uncharacteristic) to 4 (extremely characteristic). The private body
consciousness scale had the following 5 items: (1) I am sensitive to internal
bodily tensions; (2) I know immediately when my mouth or throat gets dry; (3)
I can often feel my heart beating; (4) I am quick to sense the hunger
contractions of my stomach; and (5) I'm very aware of changes in my body
temperature.

A validation study showed that patients who scored higher on the private body
consciousness scale were stimulated by caffeine (18). The instrument has been
translated and psychometrically evaluated in the Dutch population. The
evaluation of the translation resulted also in a three-factor structure and
Cronbach alpha comparable to the original test (ranging between 0.63 and
0.64) (27).

Degree of Somatic Symptoms
From the Symptom Checklist (SCL-90-R) the subscale somatization
(SCL-somatization) was used (28). This subscale rated the burden patients
experienced from a number of psychosomatic symptoms.

Information Processing Speed and Motor Speed
A simple- and a choice-reaction time task were administered to measure motor
and mental speed under two conditions. This test has been used in an aging
study of a normal population and a previous neuropsychological CFS study (2).
The aging study showed an age effect for both the motor speed and the
information processing speed measures (29).

Five target buttons were situated on a response board at equal distance around
a start button. Each target button contained a stimulus light. During the two
tasks, the subject kept the start button pressed, until a stimulus lit up. In
the first task only one stimulus button (the middle) could light up. In the
second task, three different target buttons could light up in random order. In
both tasks subjects were asked to respond as fast as possible to the button
that lit up by releasing the start button and moving to and subsequently
pressing the target button. In both conditions a distinction could be made
between speed of information processing (stimulus selection, choice selection
and response initiation) and motor speed (movement time between releasing
start button and pressing the target button). The neuropsychological test
resulted in two movement times (MT1 and MT2) and two reaction times (RT1 and
RT2).

Subjective Memory and Concentration Problems
The subscale alertness behavior of the Sickness Impact Scale (SIP alertness
behavior) (30) and the subscale Concentration of the Checklist Individual
Strength (CIS-concentration) were used to measure the degree of subjective
memory and concentration problems (15).

Validity Test-Performance
The Amsterdam Short Term Memory Test (ASTMT) is a forced choice verbal
recognition task developed to detect under performance during
neuropsychological testing (31). This test has been described in detail in a
previous study. The maximum score is 90 points (3-30 items). Validation
studies showed high average scores (> 89) for healthy subjects and patients
with mild Closed Head Injury (CHI). Based on different validation studies a
cut-off value of 86 points has been proposed (32).

Data Analysis
Structural equation-modeling techniques were used to test the model (33).
Calculations were performed with the computer program AMOS 4.0 (34). The
maximum-likelihood method of estimation was used to estimate unknown
regression parameters.

In the proposed model (Fig. 1), information-processing speed was defined as a
latent construct with the two reaction times being the measurement variables.
Information processing speed was thought to be directly influenced by body
consciousness, somatic symptom report, and age, whereas body consciousness
also had a direct effect upon somatic symptom report. For cross-validation
purposes this model was also tested with the motor speed measures and the
self-report measures as separate latent constructs.

The chi^2 statistic and the Adjusted Goodness of Fit Index were used to
test data fit. According to guidelines for structural modeling, the data were
considered to fit the model when chi^2 statistic was not significant and
Adjusted Goodness of Fit Index was high (preferably above 0.90). Furthermore,
the population error of approximation (Root Mean Square Error of
Approximation) was taken into account as measure of discrepancy per degree of
freedom. Values up to 0.05 indicate a close fit and value up to 0.08 represent
reasonable errors of approximation in the population. Preferably the 90%
confidence interval (90% CI) of the RMSEA index lies between 0.00 and 0.10
(35). When the data did not fit the model well, the modification indices
provided by the AMOS program were used to investigate whether the model could
be adjusted according theoretically valid propositions
RESULTS

Descriptives
Thirteen (23%) of the 57 patients had ASTMT scores possibly indicative of
under-performance. Hence, model testing took place in a sample of 44 subjects
(32 females and 12 males).

Table 1 depicts mean age and illness duration of this sample together with the
descriptives of the model variables. Table 2 shows the interrelations of the
model variables in this sample of 44 subjects.

Model Testing
Both the chi^2 index and AGFI index indicated good fit (chi^2=2.6;
df=8; p=0.96; AGFI=0.94). The 90% CI of the Root Mean Square Error of
Approximation also indicated a close fit of the model in relation to the
degrees of freedom (RMSEA=0.00; 90% CI, 0.00-0.00; p=0.97).

The direct relation between Body Consciousness and Information Processing
Speed did reach significance (beta=0.32; p=0.01). Level of somatic
symptom report had also a direct significant effect upon information
processing speed (beta=0.43; p<0.01), whereas Body Consciousness was
significantly related to level of somatic symptoms report (beta=0.30;
p=0.04). Education had significant relation with information processing speed
(beta=-0.25; p=0.04). However, age was not significantly related to
information processing speed (beta=0.19; p=0.12). In total, 46% of the
variance in information processing speed was explained by the model.

Testing the Model With the Motor Speed and Self Report Measures Motor Speed
The chi^2 and AGFI indices indicated good fit (chi^2=4.2; df=8; p=0.54;
AGFI=0.92). The 90% CI of the Root Mean Square Error of Approximation
indicated a less close fit of the model in relation to the degrees of freedom
(RMSEA=0.00; 90% CI, 0.00-0.11; p=0.87).

In this model, the direct relation between Body Consciousness and Motor speed
did not reach significance (beta=0.20; p=0.14), but level of somatic symptom
report did have a significant effect upon Motor Speed (beta=0.30; p=0.03).
There was a direct effect of Body Consciousness upon level of somatic symptom
report (beta=0.30; p=0.04). Age was also significantly related to motor speed
(beta=0.33; p=0.01), but education was not (beta=0.00; p=0.96). In total
27% of the variance in motor speed was explained by the model.

Experienced Memory and Concentration Problems
In this sample, the model showed reasonable fit of the data (chi^2=6.2;
df=8; p=0.77; AGFI=0.88), but the RMSEA 90% CI indicated a less close
fit in relation to the degree of freedom (RMSEA=0.00; CI, 0.00-0.15; p=0.70).
The direct relation between Body Consciousness and level of somatic
symptom report did reach significance (beta=0.32; p=0.03), and level
of somatic symptom report had a significant direct effect upon experienced
memory and concentration problems (beta=0.43; p<0.01). However, there
was no direct significant effect of Body Consciousness upon experienced memory
and concentration problems (beta=0.23; p=0.11). Age was significantly
related to experienced memory and concentration problems (beta=0.29; p=0.04),
whereas education was not (beta=0.18; p=0.20). In total 42% of the variance
in experienced memory and concentration problems was explained by the model.
DISCUSSION

In the introduction, two studies were described that reported private body
consciousness was associated with increased focusing on bodily sensations and
higher somatic symptom report, and affected information processing negatively
in nonclinical populations (19,21). Similarly, Martin et al (20) reported
that in a clinical population, body consciousness and state anxiety levels
predicted the report of symptoms. In all three studies, attentive processes
were thought to play an important role in the report of symptoms and the
processing of external information because patients with CFS report high
levels of somatically unexplained (physical) symptoms, frequently show slowing
of information processing during formal testing, and generally believe that
their illness has a physical cause (2,15,16). We hypothesized that such
information-processing models might be used to explain possible relations
between somatic symptom report and processing of external information in CFS.

The findings of this study indeed lend some support to the proposition that in
CFS attentive processes, such as private body consciousness, might affect
somatic symptom report and either directly or indirectly interfere with
external task demands. Therefore, similar mechanisms as described in the
information-processing model of Ahles et al (25) could possibly be applied to
CFS. Previous CFS research has stressed the importance of illness cognitions.
Physical causal attributions and self-efficacy were found to predict
persistence of symptoms in CFS. One could hypothesize that the conviction of
the patient that there is physically something wrong, and that one cannot
influence their complaints, does increase body consciousness and state anxiety
concerning symptoms and exertion. Instead of labeling slowing of information
processing as a direct result of cerebral impairment or deficit, it could also
be interpreted as a consequence of affective processing of symptoms or a too
strong attention for bodily sensations.

Because motor output is independent of stimuli processing, one would expect
that body consciousness or active focusing on bodily symptoms would to a less
extent associated with motor speed. The results of the model testing were in
agreement with this proposition. A previous study of our research group, using
similar tests and self-report measures, showed that there were no significant
associations between neuropsychological test performance and experienced
neuropsychological problems, but experienced neuropsychological problems were
related to both fatigue severity and depression (2). The findings of the
present study also suggest that the expression of cognitive complaints is
associated with somatic symptom report and not merely reflected in information
processing speed.

The motor planning task has been used in a cohort aging study of healthy
subjects and subjects who had biologic life event possibly affecting brain
function. In contrast to this study, age was not associated with information
processing speed. However, the aging study in which a relation between age and
information processing speed was reported, pertained to a large sample of
healthy controls who's age ranged between 17 and 84 years (29). In comparison,
our sample was relatively young, and most patients had short illness duration;
thus, there was less variation in age. It is possible that other factors than
age dominated test performances in this clinical sample. Furthermore, the
sample that provided data to test the hypothesized models was small;
therefore, the power to detect significant relationships (standardized
regression coefficients) was restricted to medium effect sizes. Our results
would gain validity when they could be replicated in other CFS samples with
different age distributions. In addition, one could verify whether similar
mechanisms as found in the current study could apply to other somatically
unexplained chronic conditions.

To what extent attentive processes play a role in CFS does need further
research. It would be interesting to compare early and late components of
somatosensory event related potentials during an experimental task in which
attention will be manipulated by a distraction task. Similarly, one could test
the effects of somatosensory stimulation upon a continuous performance task.
The clinical implications could be a therapeutic focus upon relabeling bodily
sensations, diverting attention to bodily sensations by distracting tasks, or
exposing to physical exertion to increase bodily sensations and, as such,
possibly blunt the affective response to less intense bodily stimuli. These
treatment strategies could be part of either a cognitive behavior therapy or a
graded exercise protocol, both of which have been proven effective in CFS
(36,37).
REFERENCES

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the Dutch version of the Symptom Checklist (SCL-90):Data based on a phobic
and a 'normal' population. Nederlands Tijdschrift voor de Psychologie en
haar Grensgebieden. 1981;36:77-108.